Do you want to create a set of norm "fences" that are always small when used in inline-math mode, but are allowed to grow in size as needed in display-math mode?
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MicoDec 13 '13 at 17:39

1

Not exactly. My editorial problem was the following. In inline mode, I usually use very short pieces of math (as everyone), e.g. a norm of vector v. In display mode, more complex expressions with norms appear, e.g. a product of norms of, say, five subexpressions with different size. If the size of each norm "fence" was adapted to height of the contained subexpression, then I would obtain a line of norm "fences" of significantly varying heights, what doesn't look good. Therefore, my idea was to fix the height of norm "fences" in display mode to some compromise height.
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GregoryDec 13 '13 at 20:44

Thanks for providing this additional information. I'd say @egreg's solution should be more or less what you need.
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MicoDec 13 '13 at 20:47